Perioperative fluctuations of arterial blood pressure (BP) are common and may be associated with adverse outcomes. Despite many years of research, fluctuations in blood pressure (BP), particularly hypotension due to spinal anaesthesia remains a very significant clinical problem for obstetric patients undergoing Caesarean section. This has been reported to be as high as 90% in otherwise healthy women and may be associated with serious morbidity to mother and fetus (Roofthooft & Van 2008, Smiley et al. 2006). Maternal arterial hypotension decreases uterine perfusion pressure, leading to intrapartum fetal asphyxia and fetal acidosis (Roberts et al. 1995). Severe maternal hypotension also causes maternal cerebral hypoperfusion, resulting in nausea and vomiting. Cases of intractable hypotension and cardiac arrest during spinal anaesthesia for elective caesaraen section have been described (Hawthrone & Lyons 1997, Parker et al. 1996).
Various techniques have been used to prevent and manage hypotension. The results from Cochrane database of systematic reviews showed that none of the interventions such as colloids, ephedrine, phenylephrine or lower leg compression, are effective in eliminating this condition (Cyna et al. 2006). Vasopressors are drugs commonly used to maintain BP but could lead to significant side effects. One of the difficulties is the large inter-individual variability in the severity of BP changes and their response to treatment. The use of untitrated but necessarily high doses of intravenous vasopressor phenylephrine, in conjunction with intravenous fluids, has been proposed to be nearly obviate the risk of hypotension (Ngan Kee et al. 2005) but at the expense of overtreatment (reactive hypertension and compensatory bradycardia). The impact of such an eventuality on the mother and neonate, especially in high risk patients (severe preeclampsia and intra uterine growth retardation) may not be innocuous. Moreover, injudiciously high doses of phenylephrine have been found to compromise uteroplacental circulation (Erkinaro et al. 2004) in spite of the Pyrrhic elimination of hypotension.
Hypotension, for example, blood pressure lower than about 10% of baseline physiologic value of each individual, is a very common side effect in obstetric patients undergoing Caesarean section. This could potentially induce side effects in both mother (nausea, vomiting) and fetus (acidosis) (Ngan Kee et al. 2004). However, the current standard technique using the recommended drug called phenylephrine is well known to result in overtreatment of BP, resulting in a significantly higher than normal BP (reactive hypertension, with BP greater than 20% of baseline) in more than 40% of the patients and reactive slowing of maternal heart rate (bradycardia); these may not be innocuous in high risk patients (Ngan Kee et al. 2005).
One of the main causes of overtreatment of BP is the inability to continuously and reliably measure BP non-invasively. In particular, the use of the conventional method of non-invasive BP monitoring (based on the principle of oscillometry) is limited by the time it takes to inflate and subsequently to deflate the cuffs commonly applied to the arm. The lag period and lack of a ‘real-time’ measurement of BP will lead to failure to refine and react in a timely manner to changes in BP when they occur. In spinal anaesthesia, these changes could be very drastic and sudden—if left untreated could result in negative repercussions to the mother and fetus. The use of an invasive catheter which is inserted into the artery (arterial line) is impractical and not without risk.
There remains a need to provide an alternative approach that can prevent or ameliorate the adverse clinical outcomes associated with fluctuations of BP.